Hysteresis and eddy-current losses in steel plates with nonlinear magnetisation characteristics

Hysteresis in a ferromagnetic material subjected to cyclic magnetisation is represented by an idealised elliptical B/H loop which neglects harmonic quantities and enables the flux density and the magnetising force to be related by complex permeability. The concept is then developed for steels with nonlinear magnetisation characteristics, thus permitting the computation of flux penetration and realistic losses in plates, including both hysteresis and eddy-current effects. The method described in the paper is compared with existing methods of calculating losses in steel plates, and results using these alternative methods suggest that only small errors occur by neglecting harmonic quanitites in the field quantities. Fröhlich-curve approximations tothe magnetisation characteristic are shown to be valid for thick plates at flux levels in the saturated region. Good agreement is obtained between measured and computer values for thick mildsteel plates.